High-voltage electroencephalogram spindles in rats, aging and 5-HT 2 antagonism

Abstract

We examined the effects of serotonin-2 (5-hydroxytryptamine-2, 5-HT 2) receptor antagonists on the so-called high-voltage spindles (HVS, electroencephalographic patterns, characterized by large amplitude rhythmic waves mainly in the α band), recorded from the frontal cortex of young, middle-aged and old freely-moving rats during waking immobility. The study was based on the assumption that the effects of 5-HT 2 receptor antagonists on the HVS activity depend on the age of rats, because there is evidence for an age-related decrease in the 5-HT 2 binding sites density. Four parameters of the electroencephalogram (EEG) were used to characterize the HVS activity: the square root-transformed EEG peak power in the α band, the frequency corresponding to this peak (both measured from the EEG power spectra using the fast Fourier transform), the HVS mean duration, and the HVS incidence (both measured from the EEG records). The EEG parameters were analyzed after i.p. administration of three 5-HT 2 receptor antagonists: ketanserin, ritanserin and cyproheptadine. In young rats, the three drugs increased the α power, but did not change the α peak-corresponding frequency. Ketanserin and ritanserin did not change the HVS mean duration and HVS incidence, while cyproheptadine increased both these parameters in young rats. In middle-aged and old untreated rats, the HVS activity was significantly increased. The three 5-HT 2 antagonists did not change the HVS activity in aged rats, which could be due to age-related suppression of the 5-HT 2 receptor functions.